Content providers, such as broadcasters who broadcast content, particularly media content containing video and/or audio are particularly concerned with preventing unauthorised distribution of their content. A particular problem comes from content receiving devices used by the end user or consumer, such as set-top-boxes. These devices receive broadcasts containing media content for displaying to the end user, for example on a television or other type of display. Often the user pays to receive the content, either on a regular subscription to receive particular channels, or perhaps as a one off pay-per-view event to view a particular program. Unscrupulous users may re-broadcast or otherwise make available this content to those who have not paid to view it.
A number of methods have been proposed for preventing or detecting a user re-broadcasting or forwarding content. Unfortunately these do not offer sufficient protection when the user is forwarding content from one device to another, using methods that will be elaborated on below. Without sufficient content copy protection in place, content providers may be reluctant to allow their content to be distributed using these techniques.